Thermostatic switch for electric heaters



March 12, 1957 E. L. PARR THERMOSTATIC swncn FOR ammo HEATERS FiledApril 4, 1955 BY mam HZTURNE),

United States Patent THERR IOSTATIC SWITCH FOR ELECTRIC HEATERS EdwardL. Parr, Burbank, Calif.

Application April 4, 1955, Serial No. 498,929

Claims. (Cl. 200-138) This invention relates to a thermostatic switchprimarily for use in electric heaters having air circulating fanstherein.

It is the object of the invention to provide a switch of the typereferred to which is so small and compact that it may be placed Withinthe very limited space of small heaters and ventilators, such ascommonly placed in automobiles to maintain comfortable room temperaturewithin the car while the motor is inactive. Another object is to providea switch composed of very few rigidly combined parts which may bedepended upon to give perfect service during the life of the heater.

The invention accordingly comprises novel combinations of parts whichare hereinafter fully described and a preferred form of the invention isillustrated in the accompanying drawing of which:

Fig. 1 is a cross-sectional view through the center of a switchembodying the invention;

Fig. 2 is a substantially corresponding plan view of the switch with aportion thereof partly broken away for the sake of clearness;

Fig. 3 shows one of the contact elements of the switch as it appearsbefore mounted in position therein;

Fig. 4 is an edge view of this element; and

Fig. 5 is a bottom view of the switch housing.

The particular embodiment of the invention illustrated in the drawingscomprises a cylindrical tray 1, the bottom of which is perforated toreceive therein a smaller, somewhat similarly shaped switch base orhousing 2. This housing is composed of suitable insulating material, aceramic composition having been found very convenient and inexpensive.in two diametrically opposed openings in the base of the housing aremounted conductive terminal posts 3, 4 and T-shaped terminal plates 5, 6are fastened to the outer ends of the posts.

A passage 7 is cut axially through the center of the housing base and acircular boss rises from the base in axial alinernent with the passage.This boss forms a seat for circular contact element 9. A circular curvedbimetallic member 11 is coaxially seated on the bolt above the contactelement 9 and a sleeve 12 is seated on the bolt between this member andthe contact element 9 to maintain the parts in properly spaced relationto each other on the bolt. The bimetallic member 11 normally exertssufficient pressure against the contact element 9 to insure perfectcontact with the terminal posts 3, 4. A threaded nut 13 is applied tothe bolt firmly to lock the parts in position thereon. This nut is inthe drawings shown conically shaped to provide secure clamping of theparts when the bolt is operated to draw the nut into the seat 7 which isshaped fittingly to receive the nut.

Snap switches including terminal posts, a disk for contact with theposts and a bimetallic member urging the disk into contact with theposts have been produced. The objection to this type of arrangement isthe difficulty of correctly alining the parts on the ceramic basesurface to obtain perfect contact with the posts when the bimetallicmember snaps into closing position. It has also been found that heatgenerated due to imperfect contact may cause the disk to warp and so toexaggerate this condition to such an extent no contact is made or thatan arc may form between the disk and one of the contact posts. This willdestroy the utility of the switch. Another disadvantage of this type ofswitch is that a spring must be placed behind the disk to force the diskaway from the posts when the member snaps back.

All of this is entirely overcome by shaping the contact element 9 asindicated in Figs. 3 and 4 of the drawings. The element is composed ofresilient, current conducting material and a spiral-shaped slit 15 iscut through the element. This slit extends from a point a distance fromthe central perforation 16 of the element nearly to the outer peripherythereof. The element is not flat but somewhat helically shaped,substantially as indicated in Fig. 4, and the outer rim 17 is unbrokento assure con tact with the posts in any circumferential position theelement may assume when the parts are assembled. The portion 18 of thesurface between the perforation 16 and the inner winding 19 of the slitmust be wide enough to assure firm anchoring on the bolt and the widthof the surface between the convolutions of the slit may graduallydecrease until, at the outer end of the slit, the rim is merely wideenough to provide complete contact with the end of one of the posts.When so shaped and when the element is of the proper thickness andresilience, it is found that every portion of the slitted element isfree to yield to assure perfect contact with the posts. The bimetallicelement will when a certain degree of heat is reached pop upwardly andso release the contact element for return to its normal helical shape.In the drawings two contact posts are shown, but additional posts may,if desired, be employed.

The provision of the spirally slitted helically shaped contact elementhas the further advantage that fewer parts are required than found inany thermostatic snap switch that has come to my notice and that all ofthese parts are firmly locked in position. But while the particulararrangements and shapes above outlined have been found satisfactory, itis to be understood that modifications, within the scope of the claimshereto appended, may be embodied therein without departing from thespirit of the invention.

I claim:

1. A thermostatic switch comprising, a dielectric base, contact postsseated on said base, a bolt in the center of the base rising from thesurface thereof, a circular bimetallic member mounted on the bolt, acontact element on the bolt below the member in position to contact saidposts, and means for locking the member and element in position on thebolt in correct relation to the contact posts, the element havingtherein a spirally shaped slit uniformly arranged above the centerthereof and extending nearly to the outer edge of the element.

2. A thermostatic switch comprising, a support having a circularperforation therethrough, a cylindrical housing having a shoulder at thebottom thereof seated in the perforation of the support, contact postsrising from the sur face of the housing, a bolt seated in and risingfrom the center thereof, a circular bimetallic member on the bolt, and aresilient spirally slitted contact element mounted on the bolt betweenthe member and the contact posts.

3. A thermostatic switch comprising, a support having a circularperforation therethrough, a cylindrical dielectric housing having ashoulder at the bottom edge thereof seated in the perforation of thesupport, contact posts rising from the bottom of the housing, a boltseated in and rising from the center thereof, a circular bimetallicmember mounted on the bolt, a resilient circular contact element on thebolt between the member and the posts, the element having therein aspirally formed slit uniformly placed about the center of the element,the inner end of the slit being spaced a distance away from the centerof the element, the distance between the convolutions or" the slitgradually and uniformly decreasing toward the outer end of the slit, theslitted element being helically shaped.

4. In a thermostatic switch, a circular contact element having a centralperforation and a. spirally shaped slit therethrough, the inner end ofthe slit being spaced a distance away from the center perforation andextending nearly to the periphery of the element, the distance betweenthe convolutions of the slit decreasing uniformly from the inner to theouter end thereof, the element being helically shaped.

5. A thermostatic switch comprising, a support having a circularperforation therethrough, a cylindrical dielectric housing having ashoulder at the bottom edge thereof seated in the perforation of thesupport and a central conical passage therethrough, contact posts risingfrom the bottom of the housing, a bolt seated in and rising through saidpassage, a circular resilient contact element seated on the bolt betweenthe member and the posts, the element having a spirally shaped slittherein, the element rising helically from the base, and a nut fittinglyseated in said conical passage to engage the bolt firmly to clamp themember and the element in position on the base.

References Cited in the file of this patent UNITED STATES PATENTS5l2,672 Egan Jan. 9, 1894 887,166 Wilhelm May 12, 1908 2,l99,638 Lee May7, 1940

